Boring tools for processing hard materials, such as metal work pieces, having a cutting edge formed of cBN (cubic boron nitride) material are known in the art. For example, some known cutting tools have a cBN blank which is brazed to a shank of carbide material. Particularly, boron nitride is an attractive material because it has, besides diamond, a comparatively high abrasion resistance and particularly cubic boron nitride (cBN) is the second hardest material after diamond, while showing a chemical and thermal stability that is even greater than that of diamond. A high abrasion resistance and defect resistance is particularly desirable in the processing of boreholes with small inner diameter in hard materials for exactly and reproducibly processing. Despite having a high brittleness, cBN is also very expensive. Furthermore, due to its high hardness, cBN cannot be easily processed as compared to, for instance, metal materials.
FIG. 1 schematically illustrates a known cutting tool 100 having a cutting tool insert 110 and a shank body 120. The cutting tool insert 110 is formed by a base 111 and a cutting part 113 sintered together to form a sintered body composition as indicated by the broken line in FIG. 1. The cutting tool insert 110 is fixed to the shank body 120 by brazing. Usually, the cutting tool insert 110 is allotted as a diamond sintered compact and a cBN sintered compact due to the expensive materials involved, particularly only the cutting part 113 being usually formed from cBN to provide an excellent abrasion resistance at the cutting tool insert 110.
The cutting tool insert 110 further has a rake face 112 and a first flank face 114 which define a cutting edge there between. In operation, material of a workpiece (not illustrated) fed to the cutting edge chips along the rake face 112 of the cutting tool insert 110 while an inclination of the first flank face 114 with regard to the rake face 112 provides a clearance between the cutting tool insert and a workpiece surface (not illustrated), therefore no part of the cutting tool besides the cutting edge is in contact with the workpiece. The rake face 112 extends into the shank body 120 due to a rake face 122 formed on the shank body 120. The rake face 122 of the shank body 120 represents a curved surface which is curved such that a clearance between the rake face and a workpiece (the clearance on the rake face is often referred to as “chip pocket on the rake face”) is sufficient to receive the chip and to guide the chip away from the cutting edge.
Adjacent to the first flank face of the cutting tool insert 110 a second flank face 116 of the cutting tool insert 110 is located, which a second flank face 116 extends into a flank face 124 of the shank body 120.
The rake face 112 of the cutting tool insert 110 is aligned to a centre axis A of the shank body 120. Therefore, the rake face 112 and the centre axis A1 coincide along the cutting tool insert 110, an according configuration being conventionally referred to as a “rake face with 0°”.
A cutting tool as discussed with regard to FIG. 1 is known from document JP 10128603 A.